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research-article

Subsynchronous vibration patterns under reduced oil supply flow rates

[+] Author and Article Information
Bradley R. Nichols

Rotating Machinery and Controls Laboratory Department of Mechanical and Aerospace Engineering University of Virginia Charlottesville, Virginia, 22904
brn7h@virginia.edu

Roger L. Fittro

Rotating Machinery and Controls Laboratory Department of Mechanical and Aerospace Engineering University of Virginia Charlottesville, Virginia, 22904
fittro@virginia.edu

Christopher P. Goyne

Rotating Machinery and Controls Laboratory Department of Mechanical and Aerospace Engineering University of Virginia Charlottesville, Virginia, 22904
goyne@virginia.edu

1Corresponding author.

ASME doi:10.1115/1.4038363 History: Received July 11, 2017; Revised August 31, 2017

Abstract

Reduced oil supply flow rates in fluid film bearings can cause cavitation, or lack of a fully developed hydrodynamic film layer, at the leading edge of the bearing pads. Reduced oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses; however, little experimental data of its effects on system stability and performance can be found in the literature. This study looks at overall system performance through observed subsynchronous vibration patterns of a test rig operating under reduced oil supply flow rates. The test rig was designed to be dynamically similar to a high-speed industrial compressor. It consists of a flexible rotor supported by two tilting pad bearings in vintage, flooded bearing housings. Tests were conducted over a number of supercritical operating speeds and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings. A low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain. During supercritical operation, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. Under lightly loaded conditions, the amplitude of the subsynchronous peak increased dramatically with decreasing oil supply flow rate and increasing operating speed. Under an increased load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results.

Copyright (c) 2017 by ASME
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